Epitaxial wafer and method of producing the same

ABSTRACT

An epitaxial wafer comprises a silicon substrate, a gettering epitaxial film formed thereon and containing silicon and carbon, and a main silicon epitaxial film formed on the gettering epitaxial film, in which the gettering epitaxial film has a given carbon atom concentration and carbon atoms are existent between its silicon lattices.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an epitaxial wafer and a method of producingthe same, and more particularly to an epitaxial wafer having a givengettering means suitable for an imaging device or a thin film device anda method of producing the same.

2. Description of the Related Art

As a problem in a semiconductor process is mentioned an incorporation ofa heavy metal as an impurity into a silicon wafer. If the heavy metal isincorporated, it remarkably exerts adverse influences on devicecharacteristics such as poor pose time, poor retention, poor junctionleak, insulation breakage of oxide film and the like. Therefore, it iscommon to adopt a gettering method for suppressing the diffusion of theheavy metal into a device forming (active) region at a front surfaceside of the silicon wafer.

As the conventional gettering method are known an intrinsic getteringmethod (IG method) utilizing micro defects inside the silicon wafer as agettering site (capture region) and an extrinsic gettering method (EGmethod) wherein mechanical strain is given to a surface (rear surface ofthe wafer opposite to the device forming surface by a sand blast processor the like or a polycrystalline silicon film is formed on the rearsurface as a gettering site.

With the advance of techniques for electronic devices such as mobilephones, digital still cameras and the like, it is extending to thin thethickness of semiconductor device to be built into these electronicdevices. As a result, it is demanded to develop silicon wafers in whichthe aforementioned gettering site is existent in a region closer to thedevice active layer for obtaining a high gettering ability.

However, even when the silicon wafer having the gettering site closer tothe device active layer is formed by the IG method as compared with theEG method, a DZ layer having no oxygen precipitation nucleus may beformed in a region ranging from the surface of the wafer to not lessthan 10 μm by the heat treatment. The final thickness of thesemiconductor device tends to be more thinned and will be anticipated tobe about 10 μm in the year of 2010 or later. In this case, the getteringregion is not existent in the wafer, so that metal impurities generatedat the device step can not be gettered fully. As the impuritiesgenerated in the device active layer can not be gettered sufficiently,the IG and EG methods can not be applied to the thinned device as theyare.

As the silicon wafer having the gettering site closer to the deviceactive layer is mentioned a silicon wafer as described inJP-A-H05-152304 wherein carbon ions are implanted into a surface of asilicon wafer to form a gettering layer at a shallow position from thesurface and then an epitaxial layer is grown on such an surface of thewafer. Also, there is mentioned a silicon wafer as described inJP-A-2006-216934 wherein a gettering layer containing C, Ge, Sn and/orPb is formed by CVD method or a doping method and then an epitaxiallayer is formed on the gettering layer.

In the silicon wafer produced by the method described inJP-A-H05-152304, however, it is required to use a very expensive ionimplantation apparatus, and also there are problems such as metalcontamination, generation of particles and the like due to the ionimplantation through the ion implantation apparatus itself, as well asoccurrence of defects induced in a finished epitaxial film due to theparticles. In the silicon wafer produced by the method described inJP-A-2006-216934, the gettering effect is developed through a latticestress effect introducing carbon into lattice positions, so that it isrequired to forming the gettering layer at a low temperature within atemperature range of 500-750° C. for introducing carbon into the latticepositions and hence the layer forming rate is largely lowered, which isunsuitable in the mass production. Since all of these silicon wafers inthese patent documents are produced at the low temperature growingmethod, there is a problem such as the deterioration of quality due todefects, haze and the like of the device active layer as a finalepitaxial film.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to provide an epitaxialwafer having a gettering layer with a high gettering ability withoutadversely influencing on the quality of a device active layer even whenthe gettering layer is formed in the vicinity of the device active layeras well as a method of producing the same.

In order to achieve the above object, the summary and construction ofthe invention are as follows:

(1) An epitaxial wafer comprising a silicon substrate, a getteringepitaxial film formed thereon and containing silicon and carbon, and amain silicon epitaxial film formed on the gettering epitaxial film, inwhich the gettering epitaxial film has a carbon atom concentration ofnot less than 50×10¹⁷ atoms/cm³ but not more than 1.0×10²¹ atoms/cm³ andcarbon atoms are existent between its silicon lattices.

(2) An epitaxial wafer according to the item (1), wherein the getteringepitaxial film has a thickness of 0.025-5 μm.

(3) An epitaxial wafer according to the item (1), wherein a siliconepitaxial undercoat is formed on the silicon substrate.

(4) An epitaxial wafer according to the item (1), wherein a cappingsilicon film is formed on the gettering epitaxial film.

(5) An epitaxial wafer according to the item (1), wherein at least oneof the silicon epitaxial undercoat, the gettering epitaxial film and thecapping silicon film is a low resistance film having a specificresistance of not more than 1Ω·cm.

(6) A method of producing an epitaxial wafer, which comprises a step ofgrowing a gettering epitaxial film containing silicon and carbon on asilicon substrate in a mixed gas atmosphere containing silicon andcarbon at a temperature of higher than 750° C. and a step of forming amain silicon epitaxial film on the gettering epitaxial film, in which acarbon atom concentration in the gettering epitaxial film is made to notless than 50×10¹⁷ atoms/cm³ but not more than 1.0×10²¹ atoms/cm³ andcarbon atoms are existent between silicon lattices.

(7) A method of producing an epitaxial wafer according to the item (6),wherein the gettering epitaxial film has a thickness of 0.025-5 μm.

(8) A method of producing an epitaxial wafer according to the item (6),which further comprises a step of growing a silicon epitaxial undercoatprior to the step of growing the gettering epitaxial film.

(9) A method of producing an epitaxial wafer according to the item (6),which further comprises a step of growing a capping silicon film betweenthe step of growing the gettering epitaxial film and the step of growingthe main silicon epitaxial film.

(10) A method of producing an epitaxial wafer according to the item (6),wherein at least one of the silicon epitaxial undercoat, the getteringepitaxial film and the capping silicon film is a low resistance filmhaving a specific resistance of not more than 1Ω·cm.

According to the invention, there can be provided an epitaxial waferhaving a gettering layer with a high gettering ability without adverselyinfluencing on the quality of a device active layer even when thegettering layer is formed in the vicinity of the device active layer aswell as a method of producing the same.

BRIEF DESCRIPTION ON THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein:

FIG. 1 is a flow chart illustrating production steps of an epitaxialwafer according to the invention;

FIG. 2 is a graph showing a carbon doped amount in a gettering epitaxialfilm of an epitaxial wafer prepared in Example 1; and

FIG. 3 is a graph showing a carbon concentration from a surface of acapping film in a depth direction of an epitaxial wafer prepared inExample 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, an epitaxial wafer 10 according to the invention isproduced by forming a gettering epitaxial film 40 containing silicon andcarbon (FIG. 1( c)) on a silicon substrate 20 (FIG. 1( a)) or a siliconepitaxial undercoat 30 (FIG. 1( b)) formed on the silicon substrate 20,if necessary, and forming a main silicon epitaxial film 60 (FIG. 1( e))as a device active layer on the gettering epitaxial film 40 or a cappingsilicon film 50 (FIG. 1( d)) formed on the gettering epitaxial film 40,if necessary.

The inventors have made various studies on an epitaxial wafer having agettering layer with a high gettering ability without adverselyinfluencing on the quality of a device active layer even when thegettering layer is formed in the vicinity of the device active layer,and found that when the gettering epitaxial film 40 containing siliconand carbon is formed at a film forming temperature of higher than 750°C. between the silicon substrate 20 and the main silicon epitaxial film60 and the carbon atom concentration in the gettering epitaxial film ismade to not less than 5.0×10¹⁷ atoms/cm³ but not more than 1.0×10²¹atoms/cm³, carbon atoms are introduced into positions between siliconlattices and also carbons existent in the lattices act as a getteringsite in the vicinity of the main silicon epitaxial film 60. Further, ithas been found that since the film growth can be carried out at atemperature higher than that of the conventional technique, it ispossible to form the gettering epitaxial film 40 having a highcrystallinity and a high quality without deteriorating the quality andthe occurrence of defects such as haze, dislocation and the likeresulting from the deterioration of the crystallinity in the getteringepitaxial film 40 can be suppressed by the main silicon epitaxial film60 formed thereon. As a result, the invention has been accomplished.

The thickness of the gettering epitaxial film 40 is preferable to be0.025-5 μm. When the thickness is less than 0.025 μm, there is a fearthat the sufficient gettering ability can not be obtained, while when itexceeds 5 μm, the epitaxial growing time becomes long to bring about thelowering of the productivity.

As shown in FIG. 1( b), the silicon epitaxial undercoat 30 may be formedon the silicon substrate 20, if necessary. Since the silicon epitaxialundercoat 30 acts as a buffering layer, the formation of the undercoat30 is an effective means for reducing the dislocation generated due tothe difference of lattice constant between the substrate 20 and the mainsilicon epitaxial film 60.

As shown in FIG. 1( d), the capping silicon film 50 may be formed on thegettering epitaxial film 40, if necessary. Since the capping siliconfilm 50 serves as a cover to the main silicon epitaxial film 60, theformation of the film 50 is an effective means for further suppressingthe diffusion of carbon atoms included in the gettering epitaxial film40 into the main silicon epitaxial film 60.

When the epitaxial wafer is used for an imaging device, a specificresistance of the film located below the device active layer, preferablya specific resistance of a film located below a depletion layer ispreferable to be not more than 1Ω·cm. Because, when the specificresistance of such a downside film is made low, electrons from aphotodiode are rapidly escaped to improve the electron mobility andhence the device characteristics.

The production method of the epitaxial wafer 10 according to theinvention will be described with reference to FIG. 1 below.

As shown in FIG. 1, the production method according to the inventioncomprises a step (FIG. 1( c)) of growing a gettering epitaxial film 40containing silicon and carbon on a silicon substrate 20 (FIG. 1( a)) ina mixed gas atmosphere containing silicon and carbon at a predeterminedtemperature and a step (FIG. 1( e)) of forming a main silicon epitaxialfilm 60 on the gettering epitaxial film 40.

The growth step of the gettering epitaxial film according to theinvention (FIG. 1( c)) is a step of growing the gettering epitaxial film40 made of Si, C and O on the silicon substrate 20, which is necessaryto be carried out in a mixed gas atmosphere containing silicon, carbonand oxygen at a temperature of higher than 750° C.

When the temperature exceeds 750° C., carbon atoms are introduced intopositions between silicon lattices, and hence carbons existent in thepositions between the lattices can be serves as a gettering site in thevicinity of the main silicon epitaxial film 60 and further precipitatesmade of silicon and carbon atoms having the gettering action can beformed in the epitaxial film 60. Furthermore, since the film growth canbe attained at a temperature higher than that of the conventionaltechnique, it is possible to grow the main silicon epitaxial film 60having a high quality on the film 40 without deteriorating the quality.At this moment, the size of the precipitates made of silicon and carbonis not particularly limited, and the precipitating site may be in theepitaxial film 60.

The growing method of the gettering epitaxial film 40 is notparticularly limited, but may be conducted, for example, by introducingan organic silicon-based gas such as methylsilane gas or the like and asilicon-based gas such as monosilane gas or the like into a furnacewithin a temperature range of 750-850° C. and simultaneously introducinga gas from a hydrogen gas bomb having an oxygen of a regulatedconcentration through another pipe into the furnace to grow an epitaxialfilm containing silicon, carbon and oxygen. On the other hand, within atemperature range of 800-1200° C. are introduced a silicon-based gassuch as dichlorosilane or trichlorosilane and an organic gas such astrimethylsilane or the like into the furnace.

Moreover, the growing temperature of the gettering epitaxial film 40 ispreferable to be higher than 750° C. but not higher than 1180° C. Whenthe temperature is not higher than 750° C., the epitaxial growth is notproceeding, while when it exceeds 1180° C., there is a fear thatimpurities included in the silicon substrate 20 mat be diffused into themain silicon epitaxial film 60.

The formation step of the main silicon epitaxial film according to theinvention (FIG. 1( e)) is a step of forming the main silicon epitaxialfilm 60 as a device active layer on the gettering epitaxial film 40 or acapping silicon film 50. The formation method of the main siliconepitaxial film 60 may be a method of forming a silicon film throughepitaxial growth. Also, the thickness of the main silicon epitaxial film60 may be adjusted to various levels depending upon the applications.For example, the thickness of the main silicon epitaxial film 60 may be2-5 μm in memory devices and 5-30 μm in imaging devices.

Also, it is preferable that a step of growing a capping silicon film 50(FIG. 1( d)) is conducted between the step of growing the getteringepitaxial film 40 (FIG. 1( c)) and the step of forming the main siliconepitaxial film 60 (FIG. 1( e)). The capping silicon film 50 serves as acover to the main silicon epitaxial film 60, so that the diffusion ofcarbon atoms in the gettering epitaxial film 40 into the main siliconepitaxial film 60 can be further suppressed. The formation method of thecapping silicon film 50 is not particularly limited, but includes, forexample, a formation through a chemical vapor deposition method (CVD), aformation by laminating and the like.

Moreover, it is preferable to conduct a step of forming a siliconepitaxial undercoat 30 by introducing a phosphine gas at a highconcentration (FIG. 1( b)) prior to the step of growing the getteringepitaxial film 40 (FIG. 1( c)). In this case, electrons generated from aphotodiode can be rapidly escaped from the photodiode portion by theundercoat, so that performances for an imaging device are improved. Theformation of the silicon epitaxial undercoat 30 can be carried out, forexample, by introducing the phosphine gas or diborane gas at a highconcentration in the growth of the gettering epitaxial film 40.

In addition, it is preferable that the silicon substrate 20 is subjectedto a heat treatment at about 1100° C. in a hydrogen atmosphere or in ahydrochloric acid gas atmosphere to remove native oxide or particlesfrom the surface of the substrate before the film forming steps (FIGS.1( c) and (e)). As is known, the efficiency of removing the native oxideor particles from the substrate surface can be enhanced by thehigh-temperature pretreatment prior to the epitaxial film growth.

Although the above is described with respect to only an embodiment ofthe invention, various modifications may be made within a scope of theinvention.

Example 1

There are provided eight samples (Samples 1-8) of a p-type (100) siliconwafer having a diameter of 200 mm and an initial oxygen concentration of7.0×10¹⁷ atoms/cm³ (ASTM F-121, 1979), which is sliced from a siliconingot grown by CZ method as shown in FIG. 1. Such a silicon wafer isused as an extreme-low oxygen wafer (no formation of oxygen precipitateby IG method) for the purpose of evaluating the gettering performance ofa gettering epitaxial film itself. This silicon wafer is a siliconsubstrate 20 (FIG. 1( a)), which is placed in an epitaxial growthfurnace at 800° C. and a temperature of the silicon substrate 20 israised to 1180° C. with a hydrogen gas and kept for 60 seconds.Subsequently, the temperature is lowered to 800° C., and thereaftermonosilane gas is introduced thereinto at a flow rate of 800 cm³/min toform an undercoat 30 having a thickness of 100 nm and furthermethylsilane gas is introduced at various flow rates so as to form agettering epitaxial film 40 having a thickness of 100 nm and a carbonatom concentration of a given value per each sample (atoms/cm³) (Sample1: 0, Sample 2: 5.0×10¹⁷, Sample 3: 5.0×10¹⁹, Sample 4: 2.5×10²⁰, Sample5: 6.5×10²⁰, Sample 6: 9.0×10²⁰, Sample 7: 1.0×10²¹, Sample 8:1.4×10²¹). Finally, the flow of the methylsilane gas is stopped at 800°C. and only the monosilane gas is flown to form a capping silicon film50 having a thickness of 50 nm. Then, the temperature is raised to 1100°C. and dichlorosilane gas is introduced to form a main silicon epitaxialfilm 60 having a thickness of 2 μm, whereby there is obtained anepitaxial wafers 10 for each of Samples 1-8.

With respect to the thus obtained samples, a carbon doped amount in thegettering epitaxial film 40 is measured by SIMS measuring machine. Apart of the measured results is shown in FIG. 2, from which it can beseen that the carbon doped amount of the gettering epitaxial film 40increases with the increase of the flow amount of methylsilane gas. Onthe other hand, FIG. 3 shows a result measured on a carbon concentrationfrom a surface of a capping film in a depth direction by SIMSmeasurement after the formation of the gettering film 40 and cappingfilm 50 at a flow rate of methylsilane gas of 12 cm³/min, from which itcan be seen that the carbon concentration in the gettering film is about1.8 atom % (9.0×10²⁰ atoms/cm³).

With respect to the samples, LPD having a size of not less than 0.13 μnon the wafer surface is measured by using a particle counter. As aresult, the LPD number is not less than 100 in only Sample 8 (carbonconcentration: 1.4×10²¹ atoms/cm³) flowing methylsilane gas of 20cm³/min and not more than about 50 in the other Samples 1-7.

Example 2

Epitaxial wafers 10 of Samples 1-8 are prepared under the sameconditions as in Example 1 except that a silicon epitaxial undercoat 30is grown by introducing phosphine gas at a high concentration at a stepof forming a silicon epitaxial undercoat (FIG. 1( b)). As a result ofthe evaluation on the silicon epitaxial undercoat 30 in the resultingsamples, it has been confirmed that the undercoat has a specificresistance of 0.1Ω·cm and a thickness of 100 nm.

With respect to all of the samples, LPD having a size of not less than0.13 μn on the wafer surface is measured by using a particle counter. Asa result, the LPD number is not less than 100 in only Sample 8 (carbonconcentration: 1.4×10²¹ atoms/cm³) flowing methylsilane gas of 20cm³/min and not more than about 50 in the other Samples 1-7.

Example 3

Epitaxial wafers 10 of Samples 1-8 are prepared at the same steps as inExample 1 except that the step of forming the epitaxial undercoat 30(FIG. 1( b)) is not conducted. It has been confirmed that the carbondoped amount of the gettering epitaxial film is the same as in Example 1after the measurement.

With respect to all of the samples, LPD having a size of not less than0.13 μn on the wafer surface is measured by using a particle counter. Asa result, the LPD number is not less than 100 in only Sample 8 (carbonconcentration: 1.4×10²¹ atoms/cm³) flowing methylsilane gas of 20cm³/min and not more than about 50 in the other Samples 1-7.

Example 4

Epitaxial wafers 10 of Samples 1-8 are prepared at the same steps as inExample 1 except that the step of forming the capping silicon film 50(FIG. 1( d)) is not conducted. It has been confirmed that the carbondoped amount of the gettering epitaxial film is the same as in Example 1after the measurement.

With respect to all of the samples, LPD having a size of not less than0.13 μn on the wafer surface is measured by using a particle counter. Asa result, the LPD number is not less than 100 in only Sample 8 (carbonconcentration: 1.4×10²¹ atoms/cm³) flowing methylsilane gas of 20cm³/min and not more than about 50 in the other Samples 1-7.

Example 5

Epitaxial wafers 10 of Samples 1-8 are prepared at the same steps as inExample 1 except that the step of forming the epitaxial undercoat 30(FIG. 1( b)) and the step of forming the capping silicon film 50 (FIG.1( d)) are not conducted. It has been confirmed that the carbon dopedamount of the gettering epitaxial film is the same as in Example 1 afterthe measurement.

With respect to all of the samples, LPD having a size of not less than0.13 μn on the wafer surface is measured by using a particle counter. Asa result, the LPD number is not less than 100 in only Sample 8 (carbonconcentration: 1.4×10²¹ atoms/cm³) flowing methylsilane gas of 20cm³/min and not more than about 50 in the other Samples 1-7.

Example 6

Epitaxial wafers are prepared under the same conditions as in Example 1except that the gettering epitaxial film is formed so as to have acarbon concentration of 5.0×10¹⁹ atoms/cm3 and the thickness of thisfilm is changed to 0.001 μm, 0.025 μm, 0.05 μm, 0.1 μm, 0.5 μm, 1 μm and2 μm, respectively.

Comparative Example 1

A sample of an epitaxial wafer is prepared under the same conditions asin Example 1 except that the step of forming the gettering epitaxialfilm 40 (FIG. 1( c)) is not conducted. With respect to the thus obtainedsample, LPD having a size of not less than 0.13 μn on the wafer surfaceis measured by using a particle counter, and as a result, the LPD numberis not more than 50.

Comparative Example 2

Epitaxial wafers 10 of Samples 1-8 are prepared in the same manner as inExample 1 except that the gettering epitaxial film 40 is grown at 750°C. in the formation step of the gettering epitaxial film (FIG. 1( c)).With respect to all of the samples, LPD having a size of not less than0.13 μn on the wafer surface is measured by using a particle counter,and as a result, the LPD number in all of Samples 1-8 is not less than100.

Evaluation Method

With respect to the samples obtained in Example and Comparative Exampleare evaluated the following evaluation items (1) and (2).

(1) Evaluation 1 of Gettering Ability (Determination of CarbonConcentration)

With respect to the samples obtained in Examples 1, 3 and 5 andComparative Examples 1 and 2, surface contamination with a nickelconcentration of 1×10¹² atoms/cm² is carried out by using a spin coatcontamination method. After the sample is further subjected to a heattreatment at 1000° C. for 1 hour, a selective etching (with a wright ETsolution) is conducted to evaluate a surface defect density of thesample. The evaluation results are shown in Table 1.

◯: not more than 1000 atoms/cm²

Δ: more than 1000 atoms/cm² but not more than 10000 atoms/cm²

X: more than 10000 atoms/cm²

(2) Evaluation 2 of Gettering Ability (Determination of GetteringThickness)

With respect to the sample obtained in Example 6, surface contaminationwith a nickel concentration of 1×10¹² atoms/cm² is carried out by usinga spin coat contamination method. After the sample is further subjectedto a heat treatment at 1000° C. for 1 hour, a selective etching (with awright ET solution) is conducted to evaluate a surface defect density ofthe sample. The evaluation result is shown in Table 2.

TABLE 1 Gettering Capping Silicon Surface defect density epitaxialsilicon epitaxial Sample Sample Sample Sample Sample Sample SampleSample film film undercoat 1 2 3 4 5 6 7 8 Example 1 presence presencepresence — ◯ ◯ ◯ ◯ ◯ ◯ ◯ Example 3 presence presence none — ◯ ◯ ◯ ◯ ◯ ◯◯ Example 4 presence none presence — ◯ ◯ ◯ ◯ ◯ ◯ ◯ Example 5 presencenone none — ◯ ◯ ◯ ◯ ◯ ◯ ◯ Comparative none presence presence X — — — — —— — Example 1 Comparative presence presence presence — ◯ ◯ ◯ ◯ ◯ ◯ ◯Example 2

TABLE 2 Surface defect density Gettering Capping Silicon Thickness ofepitaxial silicon epitaxial gettering epitaxial film (μm) film filmundercoat 0.001 0.025 0.1 0.5 1 2 Ex- presence pres- presence X ◯ ◯ ◯ ◯◯ am- ence ple 6

(3) LPD Evaluation of Final Epitaxial Grown Film

With respect to the samples of Examples and Comparative Examples ismeasured LPD number. The results are shown in Table 3.

◯: The number of LPD having a size of not less than 0.13 μm in the waferis not more than 50.

X: The number of LPD having a size of not less than 0.13 μm in the waferis not less than 50.

TABLE 3 Gettering Capping Silicon LPD epitaxial silicon epitaxial SampleSample Sample Sample Sample Sample Sample Sample film film undercoat 1 23 4 5 6 7 8 Example 1 presence presence presence ◯ ◯ ◯ ◯ ◯ ◯ ◯ X Example3 presence presence none ◯ ◯ ◯ ◯ ◯ ◯ ◯ X Example 4 presence nonepresence ◯ ◯ ◯ ◯ ◯ ◯ ◯ X Example 5 presence none none ◯ ◯ ◯ ◯ ◯ ◯ ◯ XComparative none presence presence ◯ — — — — — — — Example 1 Comparativepresence presence presence X X X X X X X X Example 2

As seen from the results of Table 1, all of the example samples have agood gettering effect. Furthermore, as seen from the results of Table 2,the sample of Example 6 is good in the surface defect density except forthe gettering thickness of 0.001 μm.

On the other hand, the sample of Comparative Example 2 has a getteringeffect equal to those of the example samples, but the LPD number thereofis larger than those of the example samples as seen from the results ofTable 3. Therefore, as the actual LPD is further observed by means of anatomic force microscope, LPD in the example samples is particles on theepitaxial surface, while a greater part of LPD in the sample ofComparative Example 2 is a pit-like defect or an epitaxial defect calledas stacking fault, which causes the deterioration of the devicecharacteristics. From this fact, it is understood that the sample ofComparative Example 2 is poor in the crystallinity as compared with theexample samples. This is considered due to the fact that although theepitaxial growth at 1100° C. is carried out at the formation step of themain silicon epitaxial film 60 in Comparative Example 2, since thetemperature in the growth of the gettering epitaxial film 40 is 750° C.,the crystallinity is bad and the quality of the crystal is not improvedeven in the further epitaxial growth at 1100° C.

According to the invention, even when the gettering layer is formed inthe vicinity of the device active layer, there can be provided anepitaxial wafer having a gettering layer with a high gettering abilitywithout adversely affecting the quality of the device active layer.

1. A method of producing an epitaxial wafer, comprising: growing agettering epitaxial film containing silicon and carbon on a siliconsubstrate in a mixed gas atmosphere containing silicon and carbon at atemperature of higher than 750° C.; forming a main silicon epitaxialfilm on the gettering epitaxial film, in which a carbon atomconcentration in the gettering epitaxial film is made to not less than5.0×10¹⁷ atoms/cm³ but not more than 1.0×10²¹ atoms/cm³ and carbon atomsare existent between silicon lattices; and growing a capping siliconfilm between the growing of the gettering epitaxial film and the growingof the main silicon epitaxial film.
 2. A method of producing anepitaxial wafer according to claim 1, wherein the gettering epitaxialfilm has a thickness of 0.025-5 μm.
 3. A method of producing anepitaxial wafer according to claim 1, which further comprises a growinga silicon epitaxial undercoat prior to the growing of the getteringepitaxial film.
 4. A method of producing an epitaxial wafer according toclaim 3, wherein at least one of the silicon epitaxial undercoat, thegettering epitaxial film and the capping silicon film is a lowresistance film having a specific resistance of not more than 1Ω·cm. 5.A method of producing an epitaxial wafer according to claim 1, whereinthe temperature is less than 1180° C.
 6. A method of producing anepitaxial wafer according to claim 1, wherein the capping silicon filmcomprises a low resistance film having a specific resistance of not morethan 1Ω·cm.
 7. A method for producing an epitaxial wafer according toclaim 1, wherein the capping silicon film suppresses diffusion of carbonatoms from the gettering epitaxial film into the main silicon epitaxialfilm.
 8. A method of producing an epitaxial wafer according to claim 1,wherein the capping silicon film is an undoped silicon film.